Plants that are grown for commercial sale, such as small trees and shrubs, are commonly grown in soil, or soil substitutes, held in containers. Compared with plants grown in the ground, container grown plants can be grown to marketable size quicker, they are more easily tended, they are more easily prepared and transported to market, and they can be successfully transplanted more often.
Water movement and retention characteristics of soil held in containers make maintaining a proper moisture level difficult. It is well known that the soil held by a plant container may store less water than a plant being grown in it may need. Less well understood is that soil held by a plant container can easily store more water than is healthy for a plant. For example, excess moisture in soil hosting a plant facilitates the growth of pathogenic soil organisms which attack a plant. Seedlings and young plants under such attack are said to be suffering from damping-off disease.
Damping-off is a disease condition of seedlings and cuttings. It is caused by certain parasitic fungi that invade a plant's tissues near the ground. Attack produces withering, usually associated with rotting of the stem near ground level. In general, damping-off is caused by soil-borne fungi that require moisture to survive. Such fungi thrive on excess soil moisture (i.e. damp soil) often occurring in conventional plant containers. Damping-off typically injures, and frequently kills, those plants it infests.